Schedule placement effect on indeterminate components

In non-concurrent mode, indeterminate fibers may commit in an
inconsistent state. But when they update, we should throw out the
old fiber and start fresh. Which means the new fiber needs a
placement effect.

packages/react-reconciler/src/ReactFiberBeginWork.js

@@ -707,7 +707,7 @@ function resolveDefaultProps(Component, baseProps) {
   return baseProps;
 }
 
-function updateIndeterminateComponent(
+function mountIndeterminateComponent(
   current,
   workInProgress,
   Component,
@@ -721,11 +721,9 @@ function updateIndeterminateComponent(
     // Disconnect the alternate pointers.
     current.alternate = null;
     workInProgress.alternate = null;
-    // Don't assign the `current` variable to null, though, since reconcileChildren uses the
-    // existence of current as a heuristic for whether to schedule placement
-    // effects on the children. This is super weird but reconcileChildren is
-    // deeply nested and it doesn't seem worth it to refactor for this edge
-    // case. (There are unit tests to prevent regressions.)
+    current = null;
+    // Since this is conceptually a new fiber, schedule a Placement effect
+    workInProgress.effectTag |= Placement;
   }
 
   const props = workInProgress.pendingProps;
@@ -757,47 +755,11 @@ function updateIndeterminateComponent(
         break;
       }
       case ClassComponentLazy: {
-        // This is a fork of updateClassComponent
-        let hasContext;
-        if (isLegacyContextProvider(Component)) {
-          hasContext = true;
-          pushLegacyContextProvider(workInProgress);
-        } else {
-          hasContext = false;
-        }
-        prepareToReadContext(workInProgress, renderExpirationTime);
-
-        let shouldUpdate;
-        if (workInProgress.stateNode === null) {
-          // In the initial pass we might need to construct the instance.
-          constructClassInstance(
-            workInProgress,
-            Component,
-            props,
-            renderExpirationTime,
-          );
-          mountClassInstance(
-            workInProgress,
-            Component,
-            props,
-            renderExpirationTime,
-          );
-          shouldUpdate = true;
-        } else {
-          // In a resume, we'll already have an instance we can reuse.
-          shouldUpdate = resumeMountClassInstance(
-            workInProgress,
-            Component,
-            props,
-            renderExpirationTime,
-          );
-        }
-        child = finishClassComponent(
+        child = updateClassComponent(
           current,
           workInProgress,
           Component,
-          shouldUpdate,
-          hasContext,
+          resolvedProps,
           renderExpirationTime,
         );
         break;
@@ -1521,7 +1483,7 @@ function beginWork(
   switch (workInProgress.tag) {
     case IndeterminateComponent: {
       const Component = workInProgress.type;
-      return updateIndeterminateComponent(
+      return mountIndeterminateComponent(
         current,
         workInProgress,
         Component,